fix(styles): resolve design system audit violations and touch scrolling

- Replace hardcoded px values with design tokens (--space-0h, --space-px,
  --space-1, --target-sm/md/lg) across layout, calendar, dashboard CSS
- Fix rgba(255,255,255,0.35) spinner border to use var(--color-glass-hover)
- Fix modal close icon from off-grid 18px to 16px
- Fix touch scrolling on mobile: add min-height: 0 and
  -webkit-overflow-scrolling: touch to .app-content

public/styles/dashboard.css

@@ -135,7 +135,7 @@
   color: var(--color-text-on-accent);
   font-size: var(--text-xs);
   font-weight: var(--font-weight-medium);
-  padding: 2px var(--space-2);
+  padding: var(--space-0h) var(--space-2);
   border-radius: var(--radius-full);
 }
 
@@ -186,7 +186,7 @@
   font-weight: var(--font-weight-medium);
   display: inline-flex;
   align-items: center;
-  gap: 2px;
+  gap: var(--space-0h);
   transition: opacity var(--transition-fast);
 }
 
@@ -395,7 +395,7 @@
 .meal-slots {
   display: grid;
   grid-template-columns: repeat(4, 1fr);
-  gap: 1px;
+  gap: var(--space-px);
   background-color: var(--color-border);
 }